An image reading apparatus may be provided, which reads an original document into image data by converting a light reflected from the original document into an image signal. In order to cause the image reading apparatus to read the original document into image data, a user inputs a user instruction for starting image reading through a user interface such as an operation panel. However, the image reading apparatus is not able to promptly start image reading even when the apparatus has been turned on. The image reading apparatus may need to wait until it becomes ready for image reading, thus increasing the overall time that may be necessary for image reading.